Experiments are proposed that use new methods to investigate the content of speech plans during three phases: assembly, initiation and execution of the speech plan. The range of structures that will be tested may show different patterns with respect to planning; these include noun and verb inflections, transitive verbs, motion verbs, and infinitive complements. Other experiments will attempt to shift the phase during which information of a given type is incorporated. Different theories of speech production, including the syntagma model, can be evaluated, and the space within which any theory can be considered valid narrowed, by the results of these experiments.